Shape optimization of a meniscus-adherent nanotip.

Abstract

A soluble tip can dissolve into a tip with curvature when partially immersed in a liquid. This process has been used in the manufacture of sophisticated tips. However, it is difficult to observe the dissolution process in the laboratory, and the dissolution mechanisms at the nanoscale still need to be better understood. Here we utilize molecular dynamics simulations to study the dissolution process of a meniscus-adherent nanotip. The tip apex curvature radius reaches its minimum in the intermediate state. The shape of this state is defined as the optimized shape, which can be used as the termination criterion in applications. In addition, the shape of one optimized tip can be well-fitted to a double-Boltzmann function. The upper Boltzmann curve of this function forms via the competition between the chemical potential influence and the intermolecular forces, while the formation of the lower Boltzmann curve is controlled by the chemical potential influence. The parameters of the double-Boltzmann function are strongly correlated with the nanotip's initial configuration and dissolubility. A shape factor ξ is proposed to characterize the sharpness of optimized tips. Theory and simulations show that optimized tips possess a greater ability to shield the capillary effect than common tips. Our findings elucidate the meniscus-adherent nanotip's dissolution process and provide theoretical support for nano-instrument manufacture.